- Clean all the parts in
a suitable solvent. Air dry all the parts.
- Inspect the mainshaft races for brinelling.
This is
a typical type of gear damage. Indentations occur in the circulative face,
spaced the same as the roller bodies. This kind of damage only affects
the race-shaft and gear-bore-race of the selected
gear. Affected areas can be identified on the roller bodies. This
kind of gear damage is serious due to the very high increase in radial
play on helical-cut gears. This can result in contact pattern
displacement on the mating gears and can even cause tooth failure.
- If brinelling is present, replace or repair the affected parts.
Brinelling can be caused by:
• | Vehicle related reciprocating loads: |
- | Driving at a low road speed in a high gear |
- | Defective vibration dampers on crankshaft |
- | Imbalance of the propeller shafts |
- | If diesel equipped, incorrectly
set injector pump |
- Inspect the mainshaft
for fine brinelling.
Fine brinelling is a combination of brinelling
and wear. The race surfaces are brightly polished, but show signs of consecutive
brinelling depressions.
- If fine brinelling is present, replace or repair the affected
parts. Fine brinelling can be caused by:
• | Vehicle related reciprocating loads: |
- | Driving at a low road speed in a high gear |
- | Defective vibration dampers on crankshaft |
- | Imbalance of the propeller shafts |
- | If diesel equipped, incorrectly
set injector pump |
- Inspect the mainshaft
for tribological oxidation, which is infinitely brinelled surface.
Tribological oxidation occurs in the shaft bearing races and the gear
bore races and takes the form of uniform radial wear, idler gear wear. This
does not take the form of plastic deformation, but consists entirely
of smoothing caused by material wear which results from fretting corrosion.
The race surfaces are always highly polished, with mirror quality.
- If tribological oxidation is present, replace or repair the affected
parts. Tribological oxidation can be caused by the following conditions:
• | Vehicle related reciprocating loads: |
- | Driving at a low road speed in a high gear |
- | Defective vibration dampers on crankshaft |
- | Imbalance of the propeller shafts |
- | If diesel equipped, incorrectly
set injector pump |
- Inspect the mainshaft
for traces of fretting.
If cooling or lubrication in the needle
bearings in no longer sufficient, it can lead to overheating, and cause
fretting corrosion or seizure of the bearing.
- If fretting is present, replace or repair the affected parts.
Fretting can be caused by:
• | Lubrication oil that has undergone thermal aging |
• | Incorrect oil specifications |
• | Towing the vehicle with the propeller shaft connected |
• | If diesel equipped, incorrectly
set injector pump |
- Inspect the gears for
break-in-wear, also known as running-in-wear.
Break-in-wear is not considered to be damage.
Break-in-wear usually ceases after the running-in-period
has expired, without damaging the components. Rough peaks produced
during manufacture are worn away, or to some extent, are rolled into
the surface. The surface structure, grinding and shaving marks, are
still visible.
- Inspect the gear teeth
for scratches.
Scratches are linear indentations on the flank,
running in the direction of sliding.
- If scratches are present, replace the affected parts. Scratches
can be caused by:
• | Dust and abrasive particles in the lubricating oil, including
those caused by flank contact |
• | The sliding action of the flanks |
- Inspect the gear teeth
for abrasive wear.
The marks left by the machining process are
erased from the active flank. The entire flank takes on a matte gray appearance.
Substantial changes take place in the tooth profile and clearance,
once abrasive wear has reached an advanced stage. This not only increases
the noise level, but can also cause secondary damage.
- If abrasive wear is present, replace the affected parts. Abrasive
wear is caused by:
• | Oil contamination resulting from wear or surface fatigue in other
areas of the transmission |
• | Sand, sludge, etc. penetrating into the transmission from the
outside |
- Inspect the gear teeth
for rippling or brinelling.
The polished tooth flanks show signs
of ripple-like alterations in the surface structure, which run perpendicular
to the direction of sliding, resembling a washboard.
- If rippling or brinelling is present, replace the affected parts.
Rippling or brinelling is caused by:
• | A combination of inadequate lubrication, high flank loads, and
low peripheral speeds |
• | Friction-induced vibration |
- Inspect the gear teeth
for light scoring.
Light scoring is the rough, partially porous
lines, or areas aligned in the direction of sliding. When the film of lubricant
is torn away between the flanks, this permits direct metal-to-metal
contact, causing seizure or welding. These welded zones are immediately
torn apart again, producing the damage associated with scoring. Scoring
initially occurs in areas subjected to high hertz frequency stresses,
and high sliding speeds, usually along the tooth root and tooth tip.
Light scoring only covers a portion of the flank. It is not strongly
developed, and has caused only insignificant wear after smoothing.
- If light scoring is present, replace the affected parts. Light
scoring is caused by:
• | Inadequate oil viscosity |
• | Unfavorable gear geometry |
• | Temporary lack of lubricant |
• | Faulty heat treatment of the gears |
- Inspect the gear teeth
for severe scoring.
Severe scoring is the same as light scoring,
except large areas of the tooth flank are affected. At an advanced stage,
the flank may heat up to such an extent, that localized discoloring
occurs.
- If severe scoring is present, replace the affected parts. Severe
scoring is caused by:
• | Inadequate oil viscosity |
• | Unfavorable gear geometry |
• | Temporary lack of lubricant |
• | Faulty heat treatment of the gears |
- Inspect the gears for
flank fatigue, causing gray spots.
Gray spots are localized
pittings on the flank, caused by material fatigue, and extremely fine pittings
formed on the load-bearing flanks. If they are in cluster,
they appear to the naked eye as matte gray staining. Under high magnification,
a large number of microscopic cracks become visible on the flank.
Pittings originating from these cracks, may create the appearance of
local flank wear. Most of the gray spots are located in the root zone
of the gear teeth.
- If gray spots are present, replace the affected parts. Gray spots
are caused by:
- Inspect the gear teeth
for slight pittings.
Slight pittings are pore-like areas
of individual pittings on the flank, caused by material fatigue. Usually,
slight pittings are only present in the root zone of the flank. Slight
pittings may cease after the run-in stage. A change in operating
conditions may also stop continued development of slight pitting.
- Inspect the gear teeth
for pittings.
Pittings are material fatigue on the flank. The
total pitting surface may become so large, that smooth running is considerably
impaired, or the remaining flank face, still bearing the load, will
soon be destroyed by wear.
- If pittings are present, replace the affected parts. Pitting is
caused by the following conditions:
• | Exceeding the sliding and rolling stresses for the material |
• | Incorrect oil viscosity |
• | Excessive operating temperature |
- Inspect the gears for
spalling.
Spalling is extensive, triangular pits on the flank,
that spread from a zone of gray spots, or a fine line of pits at the root.
The depth of the exposed surface is relatively constant throughout.
Further cracks may extend from the pits at an angle. In some cases,
the damage may even progress into the tip zone, causing tip damage.
- If spalling is present, replace the affected parts. Spalling is
caused by:
• | Exceeding the sliding and rolling stresses for the material |
• | Incorrect oil viscosity |
• | Excessive operating temperature |
- Inspect the gears for
overheating damage.
Signs of overheating are the gray, blue,
black discoloration of the gear, burnt oil, and reduced hardness. Due to
the reduction in hardness, there is scored, or grooved flank wear
in the direction of sliding, particularly in the tip and root zones.
If there is extreme overheating, the material softens, causing distortion
of the gear teeth, such as bent teeth and thermal deformation.
- If damage from overheating is present, replace or repair the affected
parts. Overheating is caused by:
• | Temporary or complete lack of lubrication, such as low oil level |
• | Very high peripheral speeds |
• | Insufficient tooth clearance |
- Inspect the selector teeth
of the gears for gear change damage.
The tooth edges are worn
and chipped, and in some cases, affected by plastic deformation as a result
of high shift loads, ragged edges. Such severe deformation of the
selector teeth edges will cause hard gear shift changes. The spline
flanks may also show signs of wear resembling fretting corrosion.
- If gear change damage is present, replace or repair the affected
parts. Gear change damage is caused by the following conditions:
• | Corresponding speeds of gears not adequately matched |
• | Operating the transmission incorrectly |
• | Incorrect clutch operation |
- Inspect the gears for
corrosion.
Signs of corrosion are the brown, red, or black
spots, sometimes with local material loss on the flank. If corrosion has
not caused material loss to the flank, the sliding and rolling action
of the flank can help to remove some of the corrosion.
- If corrosion is severe, replace the affected parts. Corrosion
is caused by:
• | Water or salt water entering the transmission |
• | Condensation forming under unfavorable operating conditions |
• | Oil aging and the decomposition of corrosion inhibitors |
- Inspect the idler gears
for brinelling.
This type of damage occurs on the roller races
of the idler gears. It is characterized by what appears to be the impression
of the bearing rollers. If the bearing only performs a supporting
function over a long period of time, there is not movement between
the gear and the supporting shaft, the bearing contact areas may show
signs of fretting corrosion.
- Replace any gears showing brinelling.
- Clean the countershaft
in a suitable cleaning solvent. Air dry the countershaft.
- Inspect the countershaft for cracks.
- Replace a cracked countershaft.
- Inspect the countershaft gears for the following conditions:
• | High spots, small shiny spots on the gear teeth mating surfaces,
that could cause gear noise |
- Lubricate the countershaft bearings with Synthetic Manual Transmission
Fluid GM P/N 12346190 (Canadian P/N 10953477).
- Replace the bearing assembly (1) if any of the following
conditions exist:
- Replace the bearing race, and inspect the mating parts, if the
following conditions exist:
• | Discoloration from overheating |